Acute coronary syndrome ( ACS )

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

Acute Coronary Syndrome (ACS) is driven by a critical imbalance between myocardial oxygen supply and demand, resulting in myocardial ischemia or infarction. In Type 1 myocardial infarction, the primary insult is endothelial damage through atherosclerotic plaque disruption, erosion, or fissuring, which triggers platelet aggregation and thrombus formation, leading to partial or total coronary luminal occlusion. Type 2 myocardial infarction occurs secondary to an ischemic supply-demand mismatch without acute atherothrombosis, such as from coronary artery spasm, embolism, severe anemia, or significant systemic hypotension.

When complete or near-complete occlusion occurs with inadequate collateral circulation, it results in Occlusion Myocardial Infarction (OMI), a state of ongoing ischemia that rapidly progresses to irreversible myocardial necrosis without immediate reperfusion. At the cellular level, reperfusion injury can further exacerbate myocardial damage, mediated by oxygen free radicals, calcium influx, and neutrophil activation.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Place the patient on continuous cardiac telemetry, establish intravenous (IV) access, and obtain a 12-lead ECG within 10 minutes of ED arrival.
• Resuscitation Goals: Administer supplemental oxygen only if the patient's ambient oxygen saturation is <90% (to maintain SpO2 90-94%).
• First-Line Pharmacotherapy:
• Aspirin: Administer 162-325 mg PO immediately (if not already given by EMS).
• Nitroglycerin: Give 0.4 mg sublingual or translingual for active ischemic chest discomfort, provided the systolic blood pressure (SBP) is >90 mm Hg.
• Analgesia: Administer IV morphine or fentanyl if the chest discomfort is refractory to nitroglycerin.
• Antiplatelet/Anticoagulant: Consider administration of P2Y12 inhibitors (e.g., clopidogrel, prasugrel, or ticagrelor) and antithrombins (e.g., unfractionated heparin, enoxaparin) based on cardiology consultation and specific ACS guidelines. Avoid ticagrelor if the patient has a history of intracranial hemorrhage.
• Reperfusion Targets: For STEMI or OMI, do not delay reperfusion. Target a first medical contact (FMC)-to-balloon inflation time of ≤90 minutes for Percutaneous Coronary Intervention (PCI). If PCI is unavailable and transport is prolonged, target a door-to-needle time of ≤30 minutes for fibrinolysis.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top "Can't-Miss" Differential Diagnoses:
• Aortic Dissection: Tearing midline pain radiating to the back; widened mediastinum, differential limb pressures.
• Pulmonary Embolism (PE): Pleuritic pain, focal chest pain, tachycardia, hypoxia, unilateral leg swelling.
• Esophageal Rupture (Boerhaave Syndrome): Sudden, sharp substernal pain often following forceful vomiting.
• Tension Pneumothorax: Sudden, sharp, pleuritic pain with absent breath sounds and hypotension.
• Cardiac Tamponade / Pericarditis: Positional pain, friction rub, muffled heart sounds, hypotension.
• Prioritized Diagnostic Workup:
• Serial ECGs & Cardiac Biomarkers: Obtain initial and serial high-sensitivity troponins (e.g., at 0 and 2-3 hours).
• Core Laboratory Panel: Complete blood counts, coagulation studies, and a comprehensive metabolic panel including glucose and electrolytes.
• Imaging: Obtain a portable chest x-ray within 30 minutes to evaluate for a widened mediastinum, pulmonary edema, or pneumothorax, but do not delay transport to the cath lab if STEMI is identified. Consider Coronary CT Angiography (CCTA) or provocative stress testing for select low-to-intermediate risk patients without acute ECG or biomarker findings.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• ECG Diagnostic Checklist:
• STEMI: New ST-segment elevation of >1 mm in at least two contiguous leads (except V2-V3). In V2-V3, thresholds are ≥1.5 mm for women, ≥2 mm for men >40 years, and ≥2.5 mm for men <40 years. Look for a new or presumably new Left Bundle Branch Block (LBBB).
• OMI Patterns:
• Hyperacute T Waves: Early OMI sign; symmetric and enlarged T waves (T > QRS, or >10 mm in men / >8 mm in women).
• Wellens Syndrome: Biphasic or deeply inverted T waves in V2-V3 indicating critical proximal LAD stenosis.
• De Winter Pattern: Tall symmetrical T waves with upsloping ST-segment depression >1 mm at the J point in precordial leads, and reciprocal ST elevation in aVR.
• Aslanger Pattern: Inferior STE isolated to lead III, with concomitant ST depression in V4-V6 and a positive/terminally positive T-wave.
• Posterior MI: Horizontal ST depression ≥0.5 mm in V1-V3, tall broad R waves, and upright T waves.
• Point-of-Care Ultrasound (POCUS): Perform rapid bedside echocardiography to evaluate for regional wall motion abnormalities (ischemia/infarction), right ventricular dilation/strain (PE), pericardial effusion/tamponade, or aortic root dilation (dissection).

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• HEART Score: A validated 0-10 point tool utilizing History (0-2), ECG (0-2), Age (0-2), Risk factors (0-2), and Troponin (0-2).
• Low Risk (0-3): Associated with a Major Adverse Cardiac Event (MACE) rate of ~1.7%; safe for ED discharge with short-term follow-up.
• Intermediate Risk (4-6): MACE rate of 12-17%; warrants ED observation and additional risk stratification testing.
• High Risk (7-10): MACE rate of 50-65%; warrants admission and consideration for early invasive intervention.
• HEART Pathway: Combines the HEART score with a 0- and 3-hour serial troponin strategy, offering higher sensitivity and negative predictive value for MACE than the score alone.
• EDACS-ADP: The Emergency Department Assessment of Chest Pain Score - Accelerated Diagnostic Pathway incorporates age, sex, CAD history, and pain descriptors. Low-risk patients with negative troponins at 0 and 2 hours and non-ischemic ECGs can be safely discharged.
• TIMI and GRACE Scores: Useful inpatient tools for determining the need for invasive therapy.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Cognitive Trap (The "Normal" ECG): Assuming a normal initial ECG rules out ACS. Approximately 50-60% of missed ACS patients exhibit normal or nondiagnostic ECGs on arrival, and 1-6% of ED chest pain patients with a normal ECG have an active NSTEMI.
• Cognitive Trap (The STEMI/Dissection Overlap): Administering thrombolytics or potent anticoagulants to a patient presenting with an inferior STEMI but also complaining of ripping/tearing back pain. A proximal aortic dissection can occlude the coronary ostium causing a STEMI; treating this with fibrinolysis is fatal.
• Critical Action (Serial ECGs): You must obtain serial ECGs in patients with ongoing, recurrent, or worsening chest pain to detect dynamic ST-segment or T-wave changes, which drastically increase the likelihood of ACS.
• Critical Action (Door-to-ECG): An ECG must be acquired and interpreted by a physician within 10 minutes of arrival for any patient with suspected ACS.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzwords: "Wellens Syndrome" (V2-V3 biphasic T-waves = proximal LAD lesion), "HEART Score / HEART Pathway" (Risk stratification), "Dynamic ST changes" (High-risk ACS feature).
• Classic Distractor (Low-Risk Testing): A question will describe a 44-year-old with a HEART score of 2, a negative initial troponin, and resolved symptoms, asking for the next best step. The distractor option will suggest "Admission for provocative stress testing." Explanation: Low-risk patients (HEART 0-3) do not require further cardiac testing in the ED and should be discharged to outpatient follow-up; stress testing is not indicated.
• Classic Distractor (Single Troponin): "Because the initial troponin is negative, acute coronary syndrome is ruled out." Explanation: Patients presenting soon after an infarction may have normal initial biomarkers; serial troponin testing (e.g., at 0 and 2-3 hours) is mandatory.
• Classic Distractor (Aortic Dissection Mimic): A patient lifting heavy objects presents with tearing chest pain and an inferior STEMI. The distractor offers "Aspirin and tPA." Explanation: This presentation is highly suspicious for aortic dissection causing coronary occlusion; the correct action is cardiac catheterization with an initial aortogram, as tPA would be lethal.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Initial Approach: "Given the patient's symptoms concerning for acute coronary syndrome, I will immediately establish IV access, place the patient on continuous cardiac monitoring, and obtain a 12-lead ECG within 10 minutes of arrival.".
• The Resuscitation: "I am administering Aspirin 324 mg and sublingual Nitroglycerin 0.4 mg since the patient's systolic blood pressure is greater than 90 mm Hg. I will also draw a baseline high-sensitivity troponin and a comprehensive metabolic panel.".
• The Reperfusion Pivot (If STEMI/OMI): "The ECG demonstrates ST-segment elevation in contiguous anterior leads. I am immediately activating the STEMI team and consulting interventional cardiology for primary PCI with a door-to-balloon goal of less than 90 minutes.".
• The Rule-Out Pivot (If non-diagnostic): "Because the initial ECG is non-diagnostic and the first troponin is negative, I will utilize the HEART Pathway. I am ordering a repeat ECG and a 3-hour high-sensitivity troponin. If the HEART score is 3 or less and the repeat troponin is negative, I will safely discharge the patient with short-term follow-up.".